WASHINGTON (Reuters) - The
United States on Tuesday scrambled to ease domestic concerns over mad cow
disease, quickly banning Canadian cattle and beef imports after Canada
reported its first case in a decade.

News of the mad cow case sent shock waves through the
North American food industry and commodity markets. Shares in major hamburger
chains like McDonald's Corp. and big beef processor Tyson Foods Inc. fell
on Tuesday.

U.S. Agriculture Secretary Ann Veneman said the risk
to human health and the possibility of transmission to animals in the United
States, where there has never been a reported case, was very low.

"At this time, we see no reason for any consumer
to be concerned about the safety of the food supply," she told CNN.
"In fact, I intend to eat a steak tonight."

Canada said it had found a case of bovine spongiform
encephalopathy (BSE), or mad cow disease, in the western province of Alberta.

The USDA said it has temporarily banned all ruminant
and ruminant products from Canada. Ruminants are animals with multiple
stomachs like cattle, sheep and goats.

Canada's only other case of mad cow disease was in 1993,
but the animal was imported from Britain. Its carcass was destroyed as
was its herd.

U.S. consumer groups urged the USDA to quickly impose
stronger safeguards to ensure mad cow disease did not enter the food supply.

"This incident only serves to underscore the urgent
need for the U.S. to dramatically step up its own food safety testing program
and be vigilant about checking for mad cow disease in beef," said
Michael Hansen, spokesman for Consumers Union, a consumer advocate group.

Mad cow is a chronic, degenerative disease affecting
the central nervous system of cattle. Britain, where the disease was first
diagnosed in 1986, destroyed 3.7 million cattle in the 1980s and 1990s
because of it.

A rare human form known as variant Creutzfeldt-Jakob
disease is thought to result from consuming contaminated cattle products.

There is no cure for the human form of the disease, which
has killed more than 100 people in Britain and Europe.

USDA Undersecretary J.B. Penn said the United States
would reopen its borders "fairly soon" if no other cattle tested
positive.

Canada is testing the affected Alberta herd and results
were expected within 48 hours, Penn said.

Canadian officials were investigating where the infected
cow came from. Claude Lavigne, an official with the Canadian Food Inspection
Agency, said it may have been imported or could have been given infected
feed.

Shares of McDonald's sank $1.21, or nearly 7 percent,
to close at $16.95 on New York Stock Exchange trading, making the stock
the top loser in the Dow Jones Industrial Average . Tyson Foods fell 46
cents or nearly 5 percent to $9.01.

At the Chicago Mercantile Exchange, U.S. cattle prices
were down the daily limit as traders feared beef consumption would drop.

Last year, the U.S. imported more than 1 million cattle
and about 1 billion pounds of beef from Canada, U.S. industry officials
said. This amounts to less than 5 percent of U.S. cattle slaughter and
beef production.